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The crystal and molecular structure of [η5-C5H3(SiMe3)2]2Yb(THF
Journal ofOr:gan9. metalnc Chemistry ELSEVIER
Journal of Organometallic Chemistry 512 (1996) 97-100
The crystal and molecular structure of [r/5-CsH 3(SiMe3) 2]2Yb(THF) Robin D. Rogers Department of Chemistry, Northern Illinois University,DeKalb, IL 60115, USA Received 5 June 1995; in revised form 9 August 1995
Abstract [r/S-CsH3(SiMe3)2]2Yb(THF) has been structurally characterized. The compound crystallizes in the orthorhombic space group Pbcn with a ~ 11.345(4), b = 13.552(4), c=21.185(6) A, and Dealt = 1.354 mg m -3 for Z = 4 . The Yb and O atoms reside on a crystallographic two-fold axis. The formally seven-coordinate Yb(II) ion is symmetrically coordinated to the Cp" ligands with an average Yb-C bond length of 2.67(2) ,~. The Yb-O bond length and centroid-Yb-centroid angle are 2.34(1) ,~ and 136°, respectively. The calculated effective ionic radius of the Cp" ligand, 1.59 ,~, is at the low end of those calculated for 18 Cp" lanthanide, lanthanum, or scandium compounds.
Keywords: Ytterbium; Cyclopentadienyl
1. Introduction On the occasion of Professor Marvin Rausch's 65th birthday, it is appropriate to publish a crystal structure of an organolanthanide compound. My interest in the structural chemistry of lanthanides dates back to my days in graduate school under the supervision of Jerry Atwood. One of my first collaborative efforts was working on the structures of Cp3La(THF) (Cp = r/5-CsH~-) and Cp3Y(THF) [1] prepared in Professor Rausch's labs. This developed into a collaboration which is still active today, but it also led to my own research effort aimed toward finding ways to control the f-element coordination sphere. In this report the structure of Cp~ Yb(THF) (Cp" = r/5-CsH3(SiMe3)2) is examined and compared with other Cp-like Yb(II) compounds, as well as 17 other Cp" compounds of the lanthanides, lanthanum, and scandium.
J Dedicated to Professor Marvin Rausch on the occasion of his 65th birthday. 0022-328x/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0022-328X(95)05878-8
2. Experimental
2.1. X-Ray data collection, structure determination, and refinement for Cp'2'Yb(THF) Crystals of the title compound were obtained from Andrea L. Wayda, then of A T & T Bell Laboratories in Murray Hill, New Jersey. A fragment of a much larger crystal was sealed in a glass capillary under Ar and transferred to the goniometer. The space group was determined to be the centric Pbcn from the systematic absences. The fragments available for data collection all came from one very large crystal. Each suffered from a higher than desired mosaic spread and as a result, fewer than anticipated observed data were noted. Very little data was found beyond 0 = 18 ° and data collection was carried out only to 0 = 21 °. A summary of data collection parameters is given in Table 1. Least-squares refinement with isotropic thermal parameters led to R = 0.080. The geometrically constrained hydrogen atoms were placed in calculated positions and allowed to ride on the bonded atom with B = 1.2 × Ueq (C). The methyl hydrogen atoms were included as a rigid group with rotational freedom at the
98
R.D. Rogers/Journal of Organometallic Chemistry 512 (1996) 97-100
Table 1 Crystal data and structure refinement Cp~Yb-THF dark brown/fragment C26H 50OSi4Yb 664.06 123(2) K Orthorhombic Pbcn a = 11.345(4) ,&, o~= 90° b = 13.552(4) ,~, /3 = 90° e = 21.185(6) ,~, 3' = 90° 3257(2) ~3 Volume 4 Z 1.354 (Mg m -3 ) Density (calculated) 3.034 mm- t Absorption coefficient Enral-Nonius CAD4 Diffractometer/scan /omega-2theta Radiation/wavelength Mo-K a (graphite monochrom.) /0.71073 ,~ F(000) 1360 0.40 x 0.35 x0.35 mm Crystal size ! .92o-20.99° 0 range for data collection Index ranges O 20-(1)] Absorption correction Semi-empirical from psi-scans Range of relat, transm, factors 1.00 and 0.64 Refinement method Full-matrix least-squares on F ~ SHELXS-86 I, SHELXL-93 2 Computing Data/restraints/parameters 1742/0/138 Goodness-of-fit on F 2 1.079 SHELXL-93weight parameters 0.0686, 125.6334 Final R indices [1> 2o'(1)] R1 = 0.0664, wR2 = 0.1646 RI = 0.0772, wR2 = 0.1784 R indices (all data) 0.0000(3) Extinction coefficient 4.342 and - 1.683 e,&-3 Largest diff. peak and hole Compound Color/shape Empirical formula Formula weight Temperature Crystal system Space group Unit cell dimensions (25 reflections 15 < 0 < 25)
b o n d e d carbon atom ( B = 1.2 X Ueq (C)). R e f i n e m e n t of the n o n h y d r o g e n atoms (except for C1, C4, and C13) was carried out with anisotropic temperature factors. The final values of the positional parameters are given in Table 2.
Table 2 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (,~ X 103) for Cp~Yb(THF) Atom
x/a
y/b
z/c
Ueq a
Yb Si(1) Si(2) O(I) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(ll) C(12) C(13)
0 - 1830(3) - 2880(3) 0 - 1843(12) - 2292(12) -2268(12) - 1772(12) - 1521(12) - 563(17) - 3225(15) - 1744(17) -3122(14) - 1860(14) -4301(14) 757(14) 289(14)
-752(1) - 1333(3) - 323(3) 974(8) - 1367(10) - 643(11) -971(11) - 1937(10) -2161(11) - 2043(15) - 1863(14) - 29(13) - 1237(12) 648(11) 294(13) 1631(10) 2680(11)
7500 9073(2) 6453(2) 7500 8202(6) 7781(7) 7151(6) 7182(6) 7791(7) 9387(8) 9378(7) 9346(7) 5807(7) 6175(7) 6656(8) 7122(7) 7164(7)
16(1) 24(1) 20(1) 18(3) 18(3) b 24(4) 22(4) 16(3) b 25(4) 53(5) 42(5) 49(5) 32(4) 33(4) 40(4) 27(4) 29(4) b
a U~q is defined as one third of the trace of the orthogonalized Uij tensor. b lsotropic refinement.
The Y b - C separations are e q u i v a l e n t at the 30- level and average 2.67(2) A with Y b - c e n t r o i d = 2.39 ,~. By utilizing S h a n n o n ' s effective ionic radii [15], it is possible to compare this structure to other lanthanide c o m p o u n d s c o n t a i n i n g c y c l o p e n t a d i e n y l - l i k e ligands. The effective ionic radius of Yb(II) o with a formal c o o r d i n a t i o n n u m b e r of seven is 1.08 A, resulting in a value of 1.59 ,& for the effective ionic radius of the Cp" ligand. A c o m p a r i s o n of the b o n d i n g parameters in c y c l o p e n t a d i e n y l - l i k e Yb(II) c o m p o u n d s is presented in
s,t
3. Results and discussion The structure and atom labeling scheme for the title c o m p o u n d are presented in Fig. 1. Y b and O(1) reside on a crystallographic two-fold axis, resulting in staggered Cp" rings. The° u n i q u e five m e m b e r e d ring is planar, to w i t h i n 0.01 A, with each Si atom an average 0.14 A out of this plane directed away from Yb. The two ring centroids and the o x y g e n atom give Y b an approximate trigonal planar geometry. Distortions occur as a result of steric repulsion b e t w e e n the Cp" rings. The c e n t r o i d - Y b - c e n t r o i d angle is expanded to 136 ° with c e n t r o i d - Y b - O ( 1 ) angles of 1 12 ° (Table 3).
Fig. 1. oa'r~ representation of Cp~ Yb(THF) with the atoms represented by their 50% probability thermal ellipsoids. (The hydrogen atoms have been given arbitrarily reduced radii.)
R.D. Rogers~Journal of Organometallic Chemistry 512 (1996) 97-100
99
Table 3 Comparison of bonding parameters in cyclopentadienyl ytterbium(II) compounds Compound
CN
IR
(~,) Cp'~Yb(THF) [Cp'~ Yb] Cp~Yb(THF) 2 (Cpt Bu)2Yb(THF)2 Cp~ Yb(THF) - 1/2toluene Cp~ Yb(pyridine) 2 Cp~ Yb(NH 3)(THF) Cp~ Yb (CP2(CH 2)3)Yb(THF)2
(MeOCH2CH2CP)2Yb(THF) (CpMe)2Yb(DME) (CpMe)2Yb(THF) CP2Yb(DME) Cp2Yb(DME) [(CpPPh 2)2 Ni(CO)2 ]-
M - C p (A.)
EIR-Cp
M-Cent
CentMCent (°)
Range
A
Avg.
(,~) b
(~)
1.59 1.58 1.61 1.58 1.58 1.60 1.64 1.53 1.56 --
2.39 2.374
2.42 2.440(4)
136 138 133 134 144 136 137 145 127 128
1.54 -1.58 1.52 1.57
2.41
130
7 7 8 8 7 8 8 8 8 9
1.08 1.08 1.14 1.14 1.08 1.14 1.14 1.14 1.14 --
2.65(1)-2.70(1) 2.642(6)-2.684(6) 2.64(4)-2.84(4) 2.64(2)-2.81(2) 2.643(7)-2.694(8) 2.692(7)-2.770(8) 2.70(4)-2.84(4)
0.05 0.042 0.20 0.17 0.051 0.078 0.14
2.67(2)-2.73(2) 2.707(4)-2.759(4)
0.06 0.052
2.67(2) 2.66(1) 2.75 2.72(5) 2.66(1) 2.74(4) 2.78(4) 2.665(4) 2.70(2) 2.73(2)
8 10 8 8 8
I. 14 -1.14 1.14 1.14
2.57(3)-2.78(4) 2.75(3)-2.77(3) c 2.60(3)-2.91(5) 2.63(2)-2.68(2) 2.678(5)-2.740(7)
0.21 0.02 0.31 0.05 0.062
2.68(6) 2.762(7) 2.72(8) 2.66(2) 2.71(2)
2.442 2.37 2.46 2.505
2.46 2.402 2.42
129 134 130
M-O
Ref.
(THF) (~) 2.34(1)
This study
2.42(1) 2.496(4)
[2] [3] [4] [5] [6] [7] [2] [8] [9]
2.53(2)
[10] [11]
2.426(2)
[12] [13] [14]
2.40(2) 2.431(8) 2.412(5) 2.46(3)
Yb(THF)2 Effective ionic radius for Yb 2+ in coordination number shown from Ref. [15]. b Effective ionic radius calculated for the cyclopentadienyl ligand. c Terminal "r/5-Cp ligand only.
Table 3. The effective ionic radii of the Cp-like ligands range from 1.52 A for Cp in Cp2Yb(DME) [13] to 1.64 A for Cp* (rlS-CsMe~ -) in Cp~Yb(NH3)(THF) [7]. Within the accuracy of the crystallographic determinations, there does not appear to be a consistent trend in the effective ionic radii of the Cp-like ligands. In the closely related structure, Cp~Yb(THF) • (1/2)toluene [5], the Y b - C average separation is almost
identical (2.66(1) ,~) to that in the title compound giving an effective ionic radius of 1.58 .A for the Cp* anion. An interesting comparison of the Y b - T H F interaction can be made since both of these compounds contain substituted cyclopentadienyl ligands of different electronic environment in identical geometries with almost identical M - C separations. The Y b - O distance in the electron-rich Cp* compound is 2.412(5) A,, while
Table 4 Comparison of effective ionic radius of Cp" in lanthanide compounds Compound
CN
Oxidation state
IR (,~) a
M-Cp", Avg. (.A,)
EIR-Cp" b
Ref.
[Cp'~ScCI]2 Cp~Sc(BH 4) [Cp~ La(NCMe)(DME)][BPh4] - DME [Cp~ Ce((Of)W(CO)2fp)] 2 Cp'~Ce Cp'~Ce(CNtBu) [Cp~ PrC1]2 Cp~ NdC12 Li(THF) 2
8 8 9 8 9 10 8 8 8 7 9 8 8 8 7 7 8 8
+3 +3 +3 +3 +3 +3 +3 +3 +3 +2 +3 +3 +2 +3 +2 +2 +3 +3
0.870 0.870 1.216 1.143 1.196 1.25 1.126 1.109 1.109 1.22 1.132 1.079 1.25 0.985 1.08 1.08 0.977 0.977
2.51 2.47(1) 2.83(3) 2.76(3) 2.83(4) 2.87(3) 2.76(2) 2.76(2) 2.78(2) 2.83(1) d 2.76(4) 2.72(3) 2.828 2.62 2.67(2) 2.66(1) 2.60(2) 2.63(2)
1.64 1.60 1.61 1.62 1.63 1.62 1.63 1.65 1.67 1.61 1.63 1.64 1.58 1.64 1.59 1.58 1.62 1.65
[16] [17] [18] [19] [20] [20] [ 16] [21] [22] [23] [24] [25] [2] [16] This study [2] [26] [26]
[AsPh4][Cp~NdC12] Cp'"Cp"Sm(THF) • l/2toluene c Cp~Sm [Cp'~Sm(OH)] 2 [Cp~Eu]~ [Cp~ YbCI] 2 Cp~ Yb(THF) [Cp~ Yb] ~ [Cp~ LuC1]2 [Cp'~Lu(OH)] 2
a Effective ionic radius for M n+ in coordination number and oxidation state shown from Ref. [15]. b Calculated effective ionic radius of the Cp" ligand. c Cp'" = r/CCsH2(SiMe3) 3. Cp" ligand only.
100
R.D. Rogers/Journal of Organometallic Chemistry 512 (1996) 97-100
for the title compound this same value is only 2.34(1)
L While the bond distances do not seem to bear out different steric demands of the Cp-like ligands, the range of compounds does. In the synthesis of substituted cyclopentadienyl-like compounds of Yb(II), the bulkier Cp* and Cp" ligands have resulted in the formally seven-coordinate structures mentioned above. The use of sterically less demanding ligands, like CpMe ( ' q S - C s H 4 M e - ) and Cp' (r/5-CsHa(SiMe3)-), however, have resulted in the formally ten-coordinate and polymeric (CpMe)zYb(THF) [11] and the eight-coordinate bis-THF adduct Cp~Yb(THF) 2 [3]. Eight-coordination predominates with a single example each of nine- and ten-coordination. Table 4 compares the effective ionic radius of the Cp" ligand in 18 reported Cp" compounds of the lanthanides, lanthanum, and scandium. These values range from 1.58 ,~ in [Cp~YbL [2] to 1.67 ,~ in the anionic [AsPh4][Cp~NdC12] [22]. The title compound is at the low end of this range. Despite the range in metal ion size, coordination number, and oxidation state, there is less than a 0.1 ,~ difference in the entire range of Cp" effective ionic radii.
Acknowledgment The title compound was synthesized and provided for this study by Dr. Andrea L. Wayda.
References [1] R.D. Rogers, J.L. Atwood, A. Emad, D.J. Sikora and M.D. Rausch, J. Organomet. Chem., 216 (1981) 383. [2] P.B. Hitchcock,J.A.K. Howard, M.F. Lappert and S. Prashar, J. Organomet. Chem., 437 (1992) 177. [3] M.F. Lappert, P.I.W. Yarrow, J.L. Atwood, R. Shakir and J. Holton, J. Chem. Soc., Chem. Commun., (1980) 987.
[4] Q. Shen, D. Zheng, L. Lin and Y. Lin, J. Organomet. Chem., 391 (1990) 321. [5] T.D. Tilley, R.A. Andersen, B. Spencer, H. Ruben, A. Zalkin and D.H. Templeton, lnorg. Chem., 19 (1980) 2999. [6] T.D. Tilley, R.A. Andersen, B. Spencer and A. Zalkin, lnorg. Chem., 21 (1982) 2647. [7] A.L. Wayda, J.L. Dye and R.D. Rogers, Organometallics, 3 (1984) 1605. [8] S.J. Swamy,J. Loebel and H. Schumann, J. Organomet. Chem., 379 (1989) 51. [9] D. Deng, C. Qian, F. Song, Z. Wang, G. Wu and P. Zheng, J. Organomet. Chem., 443 (1993) 79. [10] T. Jiang, Q. Shen, Y. Lin and S. Jin, J. Organomet. Chem., 450 (1993) 121. [1 l] H.A. Zinnen, J.J. Pluth and W.J. Evans, J. Chem. Soc., Chem. Commun., (1980) 810. [12] G.B. Deacon, P.I. Mackinnon, T.W. Hambley and C.J. Taylor, J. Organomet. Chem., 259 (1983) 91. [13] J. Jin, S. Jin and W. Chen, J. Organomet. Chem,, 412 (1991) 71. [14] G.B. Deacon, C.M. Forsyth, W.C. Patalinghug, A.H. White, A. Dietrich and H. Schumann, Aust. J. Chem., 45 (1992) 567. [15] R.D. Shannon, Acta Crystallogr., A32 (1976) 751. [16] M.F. Lappert, A. Singh, J.L. Atwood and W.E. Hunter, J. Chem. Soc., Chem. Commun., (1981) 1190. [17] M.F. Lappert, A. Singh, J,L. Atwood and W.E. Hunter, J. Chem. Soc., Chem. Commun., (1983) 206. [18] P.N. Hazin, J.W. Bruno and G.K. Schulte, Organometallics, 9 (1990) 416. [19] P.N. Hazin, J.C. Huffman and J.W. Bruno, J. Chem. Soc., Chem. Commun., (1988) 1473. [20] S.D. Stults, R.A. Andersen and A. Zalkin, Organometallics, 9 (1990) 115. [21] M.F. Lappert, A. Singh, J.L. Atwood and W.E. Hunter, J. Chem. Soc., Chem. Commun., (1981) 1191 [22] M.F. Lappert, A. Singh, J.L. Atwood, W.E. Hunter and H.-M. Zhang, J. Chem. Soc., Chem. Commun., (1983) 69. [23] W.J. Evans, G. Kociok-Kohn, S.E. Foster, J.W. Ziller and R.J. Doedens, J. Organomet. Chem., 444 (1993) 61. [24] W.J. Evans, R.A. Keyer and J.W. Ziller, J. Organomet. Chem., 394 (1990) 87. [25] P.B. Hitchcock, M.F. Lappert and S. Prashar, J. Organomet. Chem., 413 (1991) 79. [26] I.P. Beletskaya, A.Z. Voskoboynikov, E.B. Chuklanova, N.I. Kirillova, A.K. Shestakova, I.N. Parshina, A.I. Gusev and G.K.I. Magomedov, J. Am. Chem. Sot., 115 (1993) 3156.
Journal of Organometallic Chemistry 512 (1996) 97-100
The crystal and molecular structure of [r/5-CsH 3(SiMe3) 2]2Yb(THF) Robin D. Rogers Department of Chemistry, Northern Illinois University,DeKalb, IL 60115, USA Received 5 June 1995; in revised form 9 August 1995
Abstract [r/S-CsH3(SiMe3)2]2Yb(THF) has been structurally characterized. The compound crystallizes in the orthorhombic space group Pbcn with a ~ 11.345(4), b = 13.552(4), c=21.185(6) A, and Dealt = 1.354 mg m -3 for Z = 4 . The Yb and O atoms reside on a crystallographic two-fold axis. The formally seven-coordinate Yb(II) ion is symmetrically coordinated to the Cp" ligands with an average Yb-C bond length of 2.67(2) ,~. The Yb-O bond length and centroid-Yb-centroid angle are 2.34(1) ,~ and 136°, respectively. The calculated effective ionic radius of the Cp" ligand, 1.59 ,~, is at the low end of those calculated for 18 Cp" lanthanide, lanthanum, or scandium compounds.
Keywords: Ytterbium; Cyclopentadienyl
1. Introduction On the occasion of Professor Marvin Rausch's 65th birthday, it is appropriate to publish a crystal structure of an organolanthanide compound. My interest in the structural chemistry of lanthanides dates back to my days in graduate school under the supervision of Jerry Atwood. One of my first collaborative efforts was working on the structures of Cp3La(THF) (Cp = r/5-CsH~-) and Cp3Y(THF) [1] prepared in Professor Rausch's labs. This developed into a collaboration which is still active today, but it also led to my own research effort aimed toward finding ways to control the f-element coordination sphere. In this report the structure of Cp~ Yb(THF) (Cp" = r/5-CsH3(SiMe3)2) is examined and compared with other Cp-like Yb(II) compounds, as well as 17 other Cp" compounds of the lanthanides, lanthanum, and scandium.
J Dedicated to Professor Marvin Rausch on the occasion of his 65th birthday. 0022-328x/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0022-328X(95)05878-8
2. Experimental
2.1. X-Ray data collection, structure determination, and refinement for Cp'2'Yb(THF) Crystals of the title compound were obtained from Andrea L. Wayda, then of A T & T Bell Laboratories in Murray Hill, New Jersey. A fragment of a much larger crystal was sealed in a glass capillary under Ar and transferred to the goniometer. The space group was determined to be the centric Pbcn from the systematic absences. The fragments available for data collection all came from one very large crystal. Each suffered from a higher than desired mosaic spread and as a result, fewer than anticipated observed data were noted. Very little data was found beyond 0 = 18 ° and data collection was carried out only to 0 = 21 °. A summary of data collection parameters is given in Table 1. Least-squares refinement with isotropic thermal parameters led to R = 0.080. The geometrically constrained hydrogen atoms were placed in calculated positions and allowed to ride on the bonded atom with B = 1.2 × Ueq (C). The methyl hydrogen atoms were included as a rigid group with rotational freedom at the
98
R.D. Rogers/Journal of Organometallic Chemistry 512 (1996) 97-100
Table 1 Crystal data and structure refinement Cp~Yb-THF dark brown/fragment C26H 50OSi4Yb 664.06 123(2) K Orthorhombic Pbcn a = 11.345(4) ,&, o~= 90° b = 13.552(4) ,~, /3 = 90° e = 21.185(6) ,~, 3' = 90° 3257(2) ~3 Volume 4 Z 1.354 (Mg m -3 ) Density (calculated) 3.034 mm- t Absorption coefficient Enral-Nonius CAD4 Diffractometer/scan /omega-2theta Radiation/wavelength Mo-K a (graphite monochrom.) /0.71073 ,~ F(000) 1360 0.40 x 0.35 x0.35 mm Crystal size ! .92o-20.99° 0 range for data collection Index ranges O
b o n d e d carbon atom ( B = 1.2 X Ueq (C)). R e f i n e m e n t of the n o n h y d r o g e n atoms (except for C1, C4, and C13) was carried out with anisotropic temperature factors. The final values of the positional parameters are given in Table 2.
Table 2 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (,~ X 103) for Cp~Yb(THF) Atom
x/a
y/b
z/c
Ueq a
Yb Si(1) Si(2) O(I) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(ll) C(12) C(13)
0 - 1830(3) - 2880(3) 0 - 1843(12) - 2292(12) -2268(12) - 1772(12) - 1521(12) - 563(17) - 3225(15) - 1744(17) -3122(14) - 1860(14) -4301(14) 757(14) 289(14)
-752(1) - 1333(3) - 323(3) 974(8) - 1367(10) - 643(11) -971(11) - 1937(10) -2161(11) - 2043(15) - 1863(14) - 29(13) - 1237(12) 648(11) 294(13) 1631(10) 2680(11)
7500 9073(2) 6453(2) 7500 8202(6) 7781(7) 7151(6) 7182(6) 7791(7) 9387(8) 9378(7) 9346(7) 5807(7) 6175(7) 6656(8) 7122(7) 7164(7)
16(1) 24(1) 20(1) 18(3) 18(3) b 24(4) 22(4) 16(3) b 25(4) 53(5) 42(5) 49(5) 32(4) 33(4) 40(4) 27(4) 29(4) b
a U~q is defined as one third of the trace of the orthogonalized Uij tensor. b lsotropic refinement.
The Y b - C separations are e q u i v a l e n t at the 30- level and average 2.67(2) A with Y b - c e n t r o i d = 2.39 ,~. By utilizing S h a n n o n ' s effective ionic radii [15], it is possible to compare this structure to other lanthanide c o m p o u n d s c o n t a i n i n g c y c l o p e n t a d i e n y l - l i k e ligands. The effective ionic radius of Yb(II) o with a formal c o o r d i n a t i o n n u m b e r of seven is 1.08 A, resulting in a value of 1.59 ,& for the effective ionic radius of the Cp" ligand. A c o m p a r i s o n of the b o n d i n g parameters in c y c l o p e n t a d i e n y l - l i k e Yb(II) c o m p o u n d s is presented in
s,t
3. Results and discussion The structure and atom labeling scheme for the title c o m p o u n d are presented in Fig. 1. Y b and O(1) reside on a crystallographic two-fold axis, resulting in staggered Cp" rings. The° u n i q u e five m e m b e r e d ring is planar, to w i t h i n 0.01 A, with each Si atom an average 0.14 A out of this plane directed away from Yb. The two ring centroids and the o x y g e n atom give Y b an approximate trigonal planar geometry. Distortions occur as a result of steric repulsion b e t w e e n the Cp" rings. The c e n t r o i d - Y b - c e n t r o i d angle is expanded to 136 ° with c e n t r o i d - Y b - O ( 1 ) angles of 1 12 ° (Table 3).
Fig. 1. oa'r~ representation of Cp~ Yb(THF) with the atoms represented by their 50% probability thermal ellipsoids. (The hydrogen atoms have been given arbitrarily reduced radii.)
R.D. Rogers~Journal of Organometallic Chemistry 512 (1996) 97-100
99
Table 3 Comparison of bonding parameters in cyclopentadienyl ytterbium(II) compounds Compound
CN
IR
(~,) Cp'~Yb(THF) [Cp'~ Yb] Cp~Yb(THF) 2 (Cpt Bu)2Yb(THF)2 Cp~ Yb(THF) - 1/2toluene Cp~ Yb(pyridine) 2 Cp~ Yb(NH 3)(THF) Cp~ Yb (CP2(CH 2)3)Yb(THF)2
(MeOCH2CH2CP)2Yb(THF) (CpMe)2Yb(DME) (CpMe)2Yb(THF) CP2Yb(DME) Cp2Yb(DME) [(CpPPh 2)2 Ni(CO)2 ]-
M - C p (A.)
EIR-Cp
M-Cent
CentMCent (°)
Range
A
Avg.
(,~) b
(~)
1.59 1.58 1.61 1.58 1.58 1.60 1.64 1.53 1.56 --
2.39 2.374
2.42 2.440(4)
136 138 133 134 144 136 137 145 127 128
1.54 -1.58 1.52 1.57
2.41
130
7 7 8 8 7 8 8 8 8 9
1.08 1.08 1.14 1.14 1.08 1.14 1.14 1.14 1.14 --
2.65(1)-2.70(1) 2.642(6)-2.684(6) 2.64(4)-2.84(4) 2.64(2)-2.81(2) 2.643(7)-2.694(8) 2.692(7)-2.770(8) 2.70(4)-2.84(4)
0.05 0.042 0.20 0.17 0.051 0.078 0.14
2.67(2)-2.73(2) 2.707(4)-2.759(4)
0.06 0.052
2.67(2) 2.66(1) 2.75 2.72(5) 2.66(1) 2.74(4) 2.78(4) 2.665(4) 2.70(2) 2.73(2)
8 10 8 8 8
I. 14 -1.14 1.14 1.14
2.57(3)-2.78(4) 2.75(3)-2.77(3) c 2.60(3)-2.91(5) 2.63(2)-2.68(2) 2.678(5)-2.740(7)
0.21 0.02 0.31 0.05 0.062
2.68(6) 2.762(7) 2.72(8) 2.66(2) 2.71(2)
2.442 2.37 2.46 2.505
2.46 2.402 2.42
129 134 130
M-O
Ref.
(THF) (~) 2.34(1)
This study
2.42(1) 2.496(4)
[2] [3] [4] [5] [6] [7] [2] [8] [9]
2.53(2)
[10] [11]
2.426(2)
[12] [13] [14]
2.40(2) 2.431(8) 2.412(5) 2.46(3)
Yb(THF)2 Effective ionic radius for Yb 2+ in coordination number shown from Ref. [15]. b Effective ionic radius calculated for the cyclopentadienyl ligand. c Terminal "r/5-Cp ligand only.
Table 3. The effective ionic radii of the Cp-like ligands range from 1.52 A for Cp in Cp2Yb(DME) [13] to 1.64 A for Cp* (rlS-CsMe~ -) in Cp~Yb(NH3)(THF) [7]. Within the accuracy of the crystallographic determinations, there does not appear to be a consistent trend in the effective ionic radii of the Cp-like ligands. In the closely related structure, Cp~Yb(THF) • (1/2)toluene [5], the Y b - C average separation is almost
identical (2.66(1) ,~) to that in the title compound giving an effective ionic radius of 1.58 .A for the Cp* anion. An interesting comparison of the Y b - T H F interaction can be made since both of these compounds contain substituted cyclopentadienyl ligands of different electronic environment in identical geometries with almost identical M - C separations. The Y b - O distance in the electron-rich Cp* compound is 2.412(5) A,, while
Table 4 Comparison of effective ionic radius of Cp" in lanthanide compounds Compound
CN
Oxidation state
IR (,~) a
M-Cp", Avg. (.A,)
EIR-Cp" b
Ref.
[Cp'~ScCI]2 Cp~Sc(BH 4) [Cp~ La(NCMe)(DME)][BPh4] - DME [Cp~ Ce((Of)W(CO)2fp)] 2 Cp'~Ce Cp'~Ce(CNtBu) [Cp~ PrC1]2 Cp~ NdC12 Li(THF) 2
8 8 9 8 9 10 8 8 8 7 9 8 8 8 7 7 8 8
+3 +3 +3 +3 +3 +3 +3 +3 +3 +2 +3 +3 +2 +3 +2 +2 +3 +3
0.870 0.870 1.216 1.143 1.196 1.25 1.126 1.109 1.109 1.22 1.132 1.079 1.25 0.985 1.08 1.08 0.977 0.977
2.51 2.47(1) 2.83(3) 2.76(3) 2.83(4) 2.87(3) 2.76(2) 2.76(2) 2.78(2) 2.83(1) d 2.76(4) 2.72(3) 2.828 2.62 2.67(2) 2.66(1) 2.60(2) 2.63(2)
1.64 1.60 1.61 1.62 1.63 1.62 1.63 1.65 1.67 1.61 1.63 1.64 1.58 1.64 1.59 1.58 1.62 1.65
[16] [17] [18] [19] [20] [20] [ 16] [21] [22] [23] [24] [25] [2] [16] This study [2] [26] [26]
[AsPh4][Cp~NdC12] Cp'"Cp"Sm(THF) • l/2toluene c Cp~Sm [Cp'~Sm(OH)] 2 [Cp~Eu]~ [Cp~ YbCI] 2 Cp~ Yb(THF) [Cp~ Yb] ~ [Cp~ LuC1]2 [Cp'~Lu(OH)] 2
a Effective ionic radius for M n+ in coordination number and oxidation state shown from Ref. [15]. b Calculated effective ionic radius of the Cp" ligand. c Cp'" = r/CCsH2(SiMe3) 3. Cp" ligand only.
100
R.D. Rogers/Journal of Organometallic Chemistry 512 (1996) 97-100
for the title compound this same value is only 2.34(1)
L While the bond distances do not seem to bear out different steric demands of the Cp-like ligands, the range of compounds does. In the synthesis of substituted cyclopentadienyl-like compounds of Yb(II), the bulkier Cp* and Cp" ligands have resulted in the formally seven-coordinate structures mentioned above. The use of sterically less demanding ligands, like CpMe ( ' q S - C s H 4 M e - ) and Cp' (r/5-CsHa(SiMe3)-), however, have resulted in the formally ten-coordinate and polymeric (CpMe)zYb(THF) [11] and the eight-coordinate bis-THF adduct Cp~Yb(THF) 2 [3]. Eight-coordination predominates with a single example each of nine- and ten-coordination. Table 4 compares the effective ionic radius of the Cp" ligand in 18 reported Cp" compounds of the lanthanides, lanthanum, and scandium. These values range from 1.58 ,~ in [Cp~YbL [2] to 1.67 ,~ in the anionic [AsPh4][Cp~NdC12] [22]. The title compound is at the low end of this range. Despite the range in metal ion size, coordination number, and oxidation state, there is less than a 0.1 ,~ difference in the entire range of Cp" effective ionic radii.
Acknowledgment The title compound was synthesized and provided for this study by Dr. Andrea L. Wayda.
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